<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>
<body>
  <script>
    // 判断一个数是否是素数（素数也叫作质数）
    var num = prompt('请输入一个数');
    var prime;
    if (num > 1) {
      for (var i = 2; i < num; i++) {
        if (num % i == 0) {
          prime == false;
        }
      }
      if (prime) {
        document.write(num + '是素数');
      } else {
        document.write(num + '不是素数');
      }

    }
  </script>
</body>
</html>